The invention relates to columns such as fractional distillation column structures and, more particularly, provides an improved structure for increasing the efficiency of vapor-and-liquid contact column operation.
The patent literature as relates to bubble plates or contact devices, fractionation or rectification columns, and so forth, is quite developed though no such literature is currently known to the inventors which is directly related to the subject invention as claimed. The problem presently confronting the industry is one of increasing efficiency of a column without incurring substantial increases in fabrication and operating costs. A hint of part of what can be done by changes in internal design of columns is given in a paper generated 50 years ago at the Massachusetts Institute of Technology entitled Rectification of Binary Mixtures by W. K. Lewis, Jr., of that institution, publication date at M.I.T. April, 1936. At page 400 of such publication there is illustrated the concept that, for stacked bubble trays or contact devices, efficiency is enhanced where liquid flow is in the same direction over each tray. The publication, however, does not consider how descending reflux liquid can be conducted other than in an enclosed downcomer diagonally through the space directly between the plates; nor does it consider how the substantial vapor content in foam, of the descending reflux liquids, can escape back into the primary vapor path. Such vapor entrained in the reflux, of course, defeats some of the suggested theoretical efficiency of unidirectional reflux liquid flow over the contact trays. Also, the downcomer causes a structural obstruction in the contact chamber, further negating the suggested theoretical efficiency of unidirectional flow.
For ease of discussion of the present invention, the term "contact chamber" shall be used to describe the inner chamber separating the vertically-spaced bubble contact trays. The term "contact tray" or, generically, "contact device", shall be used to identify any one of a variety of trays used in, e.g., distillation towers and columns which can be employed in the present invention, to-wit: sieve trays, valve trays, bubble cap trays, etc. The term "downcomer" shall be used to describe the means of conducting reflux liquid from one tray, or "contact device", to the next lower tray. It shall also be used to describe the space outside the contact chamber and inside the column shell that serves for conducting descending liquid in the present invention. The term "downcomer reservoir" shall be used to describe the reflux pool held back in the downcomer for defoaming prior to entering into the next lower contact chamber prior to side draw cuts being taken.
Certain types of downcomer structures and tray designs have been suggested by a number of authorities to increase liquid flow rates and to tend to minimize loss of efficiency of vapor-and- liquid contact devices. See examples cited in Chapter 16 entitled Fractionation and Towers, Petroleum Refining Engineering, Fourth Edition at pages 480-483 and in Chapter 6 entitled New Fractionating-Tray Designs, from the work "Advances in Petroleum Refininq and Chemistry", Volume I, at pages 277-334.
No means, since the publication date of these articles, to the knowledge of the inventors, have been devised to carry forward such germ ideas to the extent of the present invention in devolving practical structure. Also, nowhere in any literature, of which the inventors are aware, is there disclosed any means or teaching whatever of accomplishing unidirectional flow across contact devices in a vertical column in a manner such that descending reflux liquid does not interfere with upwardly ascending vapors between contact trays; nor is there indicated in the prior art, of which the inventors are currently aware, of the teaching of using rectangular contact tray areas in vertical columns for maximum use of effective vapor-liquid contact, and also the teaching of fabricating substantially identical column sections of equivalent design, with each fitted with custom-engineered, rectangular contact trays so that the vertical columns herein may be made from modules to fit a needed column or tower, engineeringdesign profile. Furthermore, there is nothing in the teachings in the prior art of the concept of providing elongated ramp-type downcomer structures so as to create essentially quiescent downcomer de-foaming reservoirs prior to almost pure liquid introduction into a next succeeding contact chamber and onto its bubble tray. This increases liquid throughput capacity, aves heat energy, and reduces the need for side-stripper columns and/or processes. In short, the above discussed features and advantages makes the contact column of the present invention more cost-efficient.